1. Field of the Invention
The present invention relates to a semiconductor device having a circuit structured by a thin film transistor (hereafter referred to as TFT), and to a method of manufacturing the same. For example, the present invention relates to an electro-optical device, typically a liquid crystal display panel, and to electronic equipment with an electro-optical device installed as a component.
Note that, throughout this specification, the semiconductor device indicates general devices that can function by using semiconductor characteristics, and that electro-optical devices, semiconductor circuits, and electronic equipment are all categorized as semiconductor devices.
2. Description of the Related Art
Techniques for using semiconductor thin films (with a thickness on the order of several nm to several hundreds of nm) formed on a substrate having an insulating surface to structure a thin film transistor (TFT) have been in the spotlight in recent years. Thin film transistors are widely applied to electronic devices such as ICs and electro-optical devices, and the rapid development thereof as switching elements for image display devices is desired.
For example, the application of TFTs is being attempted in every electric circuit in a liquid crystal display device, such as pixel matrix circuits that control each of the pixels, arranged in a matrix shape, driver circuits that control the pixel matrix circuits, and in addition, logic circuits (such as processor circuits and memory circuits) which process external data signals; in all electric circuits.
Conducting materials such as Al, Ta, and Ti are conventionally used as wiring materials for the above TFT. A method is known of forming an anodic oxide film having high resistance by an anodic oxidation process on the surface of an electrode made from the above conducting materials, protecting the surface of the electrode, and insulating between semiconductor device electrodes.
In a conventional anodic oxidation process, an anode of a d.c. power supply electrode is first connected to an electrode formed on an insulating surface from a material capable of anodic oxidation. A platinum cathodic electrode is connected to an cathode of the d.c. power supply electrode, the electrode and the cathodic electrode are immersed in an anodic oxidation solution, and anodic oxidation is performed by applying a d.c. voltage between the two.
The current flowing between the anode and the cathode, and the voltage between them, generally change as shown below.
As shown in FIG. 26, conventionally the current is first controlled to be a constant value for an optional amount of time (this state is called a constant current state). An anodic oxide film then begins to form on the metallic wiring, the electrode resistance increases as the film gets thicker, and the voltage gradually increases. Note that in a fixed current state, the film thickness of the anodic oxide film is proportional to the voltage level.
Then, after reaching an arbitrary voltage level (ultimate voltage), the voltage is controlled so as to be constant (this state is referred to as a constant voltage state). Then, the amount of current begins to decrease, and the voltage is maintained at that value for several tens of minutes, and the anodic oxidation process is completed afterward. Although not shown in the figure, the voltage at the time of completion is zero.
Thus, in order to form an anodic oxide film conventionally with superior film quality and uniformity, a process in which a constant current state is shifted to a constant voltage state, is used.
However, for cases where conventional anodic oxidation is performed after forming the wiring from a material capable of anodic oxidation on a material that has poor adhesiveness to the material capable of anodic oxidation, problems such as the wiring peeling off or being destroyed develop. In particular, resin films, which have come into use in recent years as interlayer insulating films with superior levelness accompanying further refining and multiple layering in semiconductor devices, have poor adhesiveness to the anodic oxidation capable material, and the films are often peeled off. One such example of film peeling developing is shown in FIGS. 27A and 27B for the case of anodic oxidation being performed by using a conventional process after forming an electrode 4102 made from aluminum on a polyimide resin film 4101.
It is thought that one cause of the film peeling shown in FIG. 27A is that anodic oxidation does not occur uniformly, particularly at the edge of the electrode 4102, the solution wraps around into (penetrates) the bottom of the electrode 4102 during the anodic oxidation process, and that an anodic oxide film 4103 is formed under the edge of the electrode 4102. The larger the amount of wrap around (amount of penetration) X becomes, the more conspicuous the film peeling becomes. In this specification, when the distance from the point where the electrode 4102 contacts the resin film to the side face of the anodic oxide film 4103 is taken as Xa, and when the film thickness of the anodic oxide film 4103 formed on the side face of the electrode is taken as Xb, then the distance when Xb is subtracted from Xa is defined as the “amount of wrap around X”. The amount of wrap around in FIG. 27A is X=Xa−Xb=on the order of 0.6 to 0.7 μm.
A novel anodic oxidation process, in which film peeling etc. do not develop even when an anodic oxidation is performed on an electrode formed on a material film with poor adhesiveness, is thus demanded.